The present invention relates to a regulatable spring-and-damper system in a vehicle.
In German publication DE 199 61 715 A1 there is a description of a spring-and-damper system which is fitted as a spring strut between the wheel and the body of a vehicle and is configured as a hydropneumatic system with a hydraulically filled displacer, a hydraulic accumulator and two lines connecting the displacer to the hydraulic accumulator. A regulatable throttle valve is arranged in one of the lines; the other line is surrounded by a device generating a magnetic field. The entire system is filled with a magnetorheological fluid, the flow properties of which can be changed by applying a magnetic field in one of the connecting lines. In this way, a variable damping force can be regulated in the line enclosed by the magnetic-field-generating device, whereas a constant damping force is generated in the parallel-running line with the throttle device. A spring force can be regulated in the system by means of the hydraulic accumulator, which has a compressible gas volume separated from the hydraulic medium.
An additional regulating possibility is provided by the supply or discharge of hydraulic medium via the throttle device. The volumetric flow of the hydraulic medium to be supplied or discharged represents a manipulated variable by means of which an actively controlled system can be realized. However, the supply of hydraulic fluid requires considerable expenditure of energy.
The invention addresses the problem of providing a regulatable spring-and-damper system which has properties that are essentially comparable to those of an active system but which only requires low expenditure of energy.
This problem is solved according to the invention by the claimed features. The dependent claims specify expedient developments.
The regulatable spring-and-damper system according to the invention in a vehicle comprises a passive spring element and a damping element which is mounted in parallel and is configured with a damping characteristic that can be regulated in a variable manner and is determined by comparison with a reference system that can be actively regulated. The spring-and-damper system represents a semi-active replacement system which is used instead of the active reference system and has essentially the same positive properties as the reference system but requires considerably less energy.
The spring-and-damper system according to the invention comprises a software part and a hardware part, the software part representing an interface between a controller, for example for controlling a chassis, and the hardware part. The damping characteristic of the regulatable damping element can be continuously adapted in the course of operation to the current situation. Changing the damping characteristic allows generation of an overall force acting on the spring-and-damper system which is made up of a passive component—without open-loop or closed-loop control—and an active component. The current value of the damping characteristic thereby depends on a manipulated variable which would act on the final control element fitted in the equivalent, active reference system. Since, in the spring-and-damper system according to the invention, this manipulated variable is used solely for calculating the way in which the damping element is regulated, but need not be physically implemented in the spring-and-damper system, significant advantages in terms of energy and structural design are obtained, since no expenditure of energy has to be provided for the supply and discharge of the medium corresponding to the manipulated variable, and accordingly no structural device required for this has to be provided either. Rather, it is sufficient to influence the damping element of the system according to the invention by changing the damping characteristic. The laws governing the way in which the damping characteristic is to be regulated are based on a comparison of the mathematical behavior of the active reference system with that of the semi-active system.
Since the spring-and-damper system according to the invention has a behavior equivalent to that of the active reference system it is intended to replace, existing control strategies and approaches can be transferred directly to the system according to the invention. It is not absolutely necessary to develop new or adapted control strategies. In connection with the interface, the semi-active system has the same, or at least approximately the same, functionality as the corresponding active system.
The spring-and-damper system according to the invention merely comprises a passive spring element and a damping element which is mounted in parallel with the latter and has a damping characteristic that can be regulated in a variable manner, irrespective of the construction of the active spring-and-damper system to be replaced. Both mechanical and hydraulic, pneumatic or mixed systems come into consideration, both in respect of the active system to be replaced and in respect of the semi-active spring-and-damper system actually used. The degree of complexity of the active system to be replaced is immaterial here; a different behavior on the part of the active system is taken into account via the interface and the function calculated there for the damping characteristic, so that the semi-active spring-and-damper system can always have the same construction.
A hydropneumatic system with a displacer and a hydropneumatic spring accumulator as the spring element is advantageously used as the semi-active spring-and-damper system, the hydraulic damper communicating with the hydraulic side of the spring accumulator via a connecting line in which a regulatable throttle is arranged. By changing the throttle cross section, the damping value can be changed.
To avoid low-frequency or quasi-steady components entering the calculation of the damping characteristic, the signal representing the manipulated variable can be subjected to high-pass filtering, in which frequencies in the signal above a predeterminable cutoff frequency are eliminated.
To repeat the essential idea of the invention in a general form: the regulatable spring-and-damper system according to the invention in a vehicle comprises a spring element and a damping element which is mounted in parallel with it, one of the elements being configured in an adjustable manner. To realize a semi-active system, the spring element is passive and the damping element is configured with a damping characteristic that can be regulated in a variable manner. The semi-active system can be described according to a force profile which can be represented as a function of a variable describing the spring constant of the passive spring element and/or of a variable describing a damping value that can be regulated in a variable manner and/or of a variable describing a state variable of the system and/or of a variable describing the derivative with respect to time of the state variable. The damping element is regulated by the damping value following at least approximately a relationship which can be represented as a function of the variable describing the spring constant of the passive spring element and/or of a manipulated variable and/or of a variable describing the derivative with respect to time of the manipulated variable and/or of the variable describing the state variable of the system and/or of the variable describing the derivative with respect to time of the state variable. This relationship is based here on a function which is known from an actively regulatable reference system with an adjustable final control element. The force profile of the reference system can be described according to a relationship which can be represented as a function of the manipulated variable and/or of the variable describing the derivative with respect to time of the manipulated variable and/or of the variable describing the state variable of the system and/or of the variable describing the derivative with respect to time of the state variable, with the manipulated variable and/or the variable of the adjustable final control element describing the derivative with respect to time of the manipulated variable being determinable in a closed-loop and open-loop control unit according to a stored mathematical relationship. The spring-and-damper system represents a semi-active replacement system which is used instead of the active reference system and has essentially the same positive properties as the reference system but requires considerably less energy.
Further advantages and expedient configurations can be taken from the further claims, the description of the figures and the drawings.